Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

Browse

Filters

2009 - 200922010 - 202024

Settings

Author: search.filters.author.Özkol, ÜnverPublisher: search.filters.publisher.Izmir Institute of Technology

Search Results

Now showing 1 - 10 of 26
  • Master Thesis
    Experimental Investigation of the Pressure Drop Performance and the Cavitation of a Plunger Valve
    (Izmir Institute of Technology, 2020) Aydeniz, Emre; Özkol, Ünver
    This thesis, realized within the scope of a TUBITAK project of DOĞUġ VANA A.ġ, is aimed to characterize the pressure drop and cavitation performance of plunger valve with various cavitation lattices in different opening ratios. Pressure drop performance and cavitation studies have been examined experimentally. Loss coefficients and flow coefficients were used to examine the pressure drop performance of four different types of cavitation lattices. According to the results of this experimental study, it was observed that the loss coefficient is almost independent of Reynolds number except for Re < 4x105. Cavitation creates vibration and noise in high-frequency ranges. Therefore, cavitation detection was examined in the high-frequency range of 5 kHz to 18 kHz and was performed using an accelerometer. Fourier Transform (FT) and Power Spectrum Density (PSD) were used to measure the energy levels of vibrations. Cavitation limits (incipient and critical cavitation) were detected by comparing PSD levels and cavitation indexes at different aperture ratios for all lattices. As a result, the safe cavitation range for the valve was determined by comparing the cavitation indexes according to the valve opening ratio. A new cavitation index estimation study was performed for the new diameter and upstream pressure values with the effect of size scaling and pressure scaling.
  • Master Thesis
    Experimental Spray Investigation of Methyl Ester and Ethyl Ester Type Biodiesel Fuels in a Constant Volume Combustion Chamber
    (Izmir Institute of Technology, 2020) Ulu, Anılcan; Özkol, Ünver; Yıldız, Güray
    Biodiesel fuels are promising fuels that can reduce pollutant emissions from diesel engines. Therefore, they are still being investigated in every aspect. In this study, it was aimed at comparing the spray characteristics of methyl ester and ethyl ester type biodiesel fuels with those of fossil diesel fuel. Besides, this study aimed to investigate the spray characteristics of ethyl esters on which few studies have been done, and to help eliminate this gap in the literature. For these purposes, 4 different methyl esters from corn, sunflower, canola and cotton oils, and 2 different ethyl esters from corn and sunflower oils were produced. Commercial diesel fuel was used to compare the characteristics of these fuels. Firstly, physical properties of the fuels produced were investigated to better understand the spray investigation, and it was observed that biodiesel fuels had bigger density and viscosity values than fossil diesel fuel. Additionally, it was found that methyl esters had larger density and smaller viscosity values than ethyl esters. After that, spray characteristics of all fuels were investigated in a constant volume combustion chamber under ambient pressures of 0, 5 and 10 bar, and injection pressures of 600 and 800 bar. Then, these fuels were cnompared to each other. After the experiments, biodiesel fuels were found to have longer spray penetration lengths and narrower spray angles than diesel fuel, although there were no significant differences between them. This may be due to higher density and viscosity values of biodiesel fuels. Furthermore, no significant distinctions were found between the spray characteristics of ethyl esters and methyl esters. In addition, it was observed that ambient and injection pressures were important parameters affecting the spray pattern. As a result, it was obtained that biodiesel-air mixing was slightly worse than diesel-air mixing. However, their potential to reduce pollutant emissions may cause this difference to be ignored. Moreover, it was found that ethyl esters had similar spray characteristics as methyl esters. Hence, ethyl esters are promising to replace methyl esters.
  • Master Thesis
    Scaled Down Modelling of a Horizontal Wind Turbine for a Floating Wind Turbine Research
    (Izmir Institute of Technology, 2020) Erol, Serkan; Özkol, Ünver
    Floating wind turbines have to operate under the influence of hydrodynamic and aerodynamic forces which are usually coupled in nature. Due to complicated interactions of wave and wind forces on its structure, predicting motion and performance of a floating wind turbine usually depend on many assumptions. In order to understand the dynamics of the system, experimental studies are required to obtain results by taking into account all parameters. This study is a part of a Tübitak project (217M451) that investigates the dynamics of different floating platforms with a wind turbine attached to it under an atmospheric boundary layer wind profile. In this thesis, a scaling methodology was used to model a wind turbine to use in experimental studies. Reynolds number discrepancy was demonstrated in floating wind turbine modeling. For this reason, the method was created by using Froude number and tip speed ratio similitude, and geometric, kinematic and dynamic similarity was achieved. According to the created methodology, an onshore wind turbine that has 320kW nominal power was scaled down to be used in experimental studies according to the open sea conditions. Along with the model turbine, a thrust force measuring mechanism, hot-wire sensor travers system and a motion detection method by a video have been realized. A wave maker and a wind nozzle which are the part of the Tübitak project of which the model turbine described in this thesis will be used, therefore; small description of those are also given in the thesis.
  • Master Thesis
    Airfoil Boundary-Layer Stability Calculations and Transition Prediction
    (Izmir Institute of Technology, 2019) Pekdüz, Umut; Özkol, Ünver
    This study involves research and understanding of airfoil laminar boundary-layer transition based on three codes in written FORTRAN: panel code, boundary-layer code and stability code, namely HSPM, BLP2D and STP2D. All codes were connected to each other via inputs-outputs in the one code, called as PBS code. Firstly, the inviscid pressure distribution was obtained using Hess-Smith panel method. Secondly, differential boundary-layer equations were solved for obtained inviscid pressure distribution from panel code. Thirdly, stability calculation was performed using obtained boundary velocity profiles from boundary-layer code at each streamwise stations. Finally, the onset of transition location was predicted using en method based on linear small-disturbance theory. The PBS code was first validated on NACA 0012 and NACA 0015 airfoils making comparison with an experimental work in literature. After validation, three different thick airfoils designed for wind turbine applications were analyzed in terms of lift coefficient and transition location, namely NACA 64-618, DU91W250 and DU4050. The results were compared with XFoil’s viscous and inviscid solutions and experimental measurements based on infrared thermography. It was seen that amplified disturbance frequency magnitude, amplification starting point and choice of threshold value are key points to correctly predict transition point for en method. Additionally, it was found that followings: First, as airfoil thickness increases, the need of interactive boundary-layer method increases for accurate lift coefficient; however, transition point can be still correctly predicted using inviscid pressure distribution. Second, at high angle of attacks and high Reynolds numbers, laminar boundary-layer separation point can be directly taken as transition point instead of using the en method.
  • Master Thesis
    Spray Characterization for Water-In Emulsions
    (Izmir Institute of Technology, 2019) Çellek, Seven Burçin; Özkol, Ünver
    As we consider the pollutions caused by combustion engines, they have a big impact on several problems like global warming, acid rain, etc. Engineers and scientists are willing to control the pollutants and to reduce them as low as possible. There are some possible solutions to reduce environmental problems such as diesel particulate filters, high pressure fuel injection equipment, and sophisticated piezo injectors and associated control systems. However, all mentioned solutions need a modification on the current engine system to be used. Because of high costs of modification, recently, fuel-based solutions are more popular. This study investigates one of the possible fuel-based solutions which is water-in-diesel emulsions. Through the work, spray characteristics such as spray penetration and spray angle have been examined and compared with neat diesel spray. In order to achieve the purpose of this research, experiments have been carried out in a constant volume combustion chamber and all have been recorded by the help of a high-speed camera. A Matlab algorithm has been developed to analyse the recorded data. It was found that, due to lower volatility of the water, water-in-diesel emulsion has longer and wider spray when compared to neat diesel spray. According to the literature, this results in better fuel-air mixing for combustion process, hence cleaner exhaust gas.
  • Master Thesis
    Investigation of Co and Co2 Emissions From a Domestic Gas Burner
    (Izmir Institute of Technology, 2019) Özsüer, Alpay; Özkol, Ünver
    In this study, performance of a domestic gas burner from a gas cooktop will be evaluated. Compared to the induction and radiant cooktops, gas cooktops are less efficient, and they cause indoor air pollution. Air pollution is a global hot topic and fossil fuels are one of the biggest sources of it. Natural gas is widely used throughout the world and with this wide usage, gas cooktops are still preferred since it is also cheaper than electricity in some countries. Even though air pollution is a hot topic, the lack of indoor air quality regulations makes pollutant emissions from gas sources dangerous to human health. Even if a small improvement in efficiency or pollutant emission rate is performed, it will lead to a large impact on the global natural gas consumption or global air pollution. The aim of this study is to see effects of changing loading height on domestic gas burners. To make observations, experimental studies, which will be supported by numerical studies, will be performed according to requirements of European Norm.
  • Master Thesis
    Design and Numerical Analyses of Guide Vanes of a Multistage Submersible Pump
    (Izmir Institute of Technology, 2019) Demirtaş, Mert; Özkol, Ünver
    The objective of this thesis is to analyze a multistage submersible pump numerically, figure out the inefficient sections of flow and propose a modified design according to the simulation results. Hydraulic parts of a submersible pump are impeller, diffuser and return channel. In this study, the investigated pump’s stages have only impellers and return channels. According to the literature, the inefficiencies in pump stages might be caused by angle misalignment of impeller and guide vanes, channel geometries or vane designs. The investigated five stage submersible pump and its CAD models are provided by a manufacturing company. In the first part of the study, fluid domain is created for numerical computations and analyses are performed with ANSYS Fluent software. According to the simulation results, flow nonuniformities are observed in return channels and identified that the reason is guide vane geometry. The second part of the study includes the modified design of guide vane and set of simulations with different wrap angles to find out the optimized value. The simulation results of this thesis study are quite satisfactory when they are compared to experimental data of manufacturing company. After modifications, the nonuniformities which are observed in original design are diminished and efficiency of the pump is increased.
  • Master Thesis
    Theoretical Performance Optimization of Solar Absorption Chiller Coupled To Underground Cooling Tower
    (Izmir Institute of Technology, 2018) Ouedraogo, Kiswendsida Elias; Toprak, Kasım; Özkol, Ünver
    The study aims to enhance the thermal/economic performance of a solar powered absorption heat pump used for the cooling/heating of a shopping center in Izmir. MATLAB and TRNSYS are used to simulate the system. First, borehole thermal energy storage is added to the system to store the heat rejected by the chiller condenser in summer for later use in winter. Secondly, cooling water out of a condenser is partially stored during an 8:00-16:00 working time, and cooled from 16:00 to 8:00 to take advantage of the lower ambient temperature at night. Lastly, chilled water storage is added to the system to level the cooling load. The study revealed that the borehole efficiency is 37%. Also, it enhanced the solar fraction in winter by 40% and increased the system cooling load to heat input ratio by 110%. The second study showed that operating a cooling tower at night can reduce cooling water temperature by 5°C. In the last study, producing chilled water 24h/day reduced the required cooling capacity of the chiller to 34% of its current capacity of 1020kW, thus increasing the capacity factor from 41% to 96%. A brief economic analysis showed that the levelized cost of cooling/heating is 0.034$/kWh and 0.049$/kWh for the system with chilled water storage and the system without chilled water storage respectively. This represented a cost reduction of 29%.
  • Master Thesis
    Steady and Unsteady Aerodynamic Analysis of the Airfoil Profiles by Using Vortex Singularity Elements
    (Izmir Institute of Technology, 2018) Elmacı, Salim Cenk; Özkol, Ünver; Özbahçeci, Bergüzar
    The steady and unsteady 2D flows around the airfoil were analyzed by utilizing the vortex singularity elements with two different inviscid flow models. Firstly, the steady flow was modeled in the light of steady state algorithm available in the literature. Then, the unsteady flow model was developed by some modifications on the algorithm of the steady flow. All the algorithms were transformed to the code in MATLAB® 2018a environment. For the steady state model, lift coefficients were compared with the inviscid and inviscid-viscous coupling models of the Xfoil 6.9 program data (Drela, 2001); and NASA experimental archive (Ira Herbert Abbott & Von Doenhoff, 1959). Since the model is inviscid, the reference point is the inviscid solvers; and the model agreed well with the Xfoil 6.9 inviscid mode for different type of airfoils. The unsteady model was created with three different operating modes; which are the sudden forward, heaving and the pitching. For the sudden forward motion, the lift and drag coefficients were compared with the studies in the literature. Besides, the lift, drag moment coefficients; and the wake patterns of the heaving and pitching motions were compared with the experimental data in the literature. The model is limited in terms of reflecting lift, drag and moment coefficients due to the not being included the viscous effects, flow separation, stall etc.; however, in terms of capturing the wake patterns, the model is quite useful.
  • Master Thesis
    Investigation of Liquid Transport in Micro and Nanoscale Porous Media at Different Pore To Throat Size Ratios
    (Izmir Institute of Technology, 2017) Kalyoncu, Gülce; Barışık, Murat; Özkol, Ünver
    Extensive usage of micro/nanoscale porous media in various applications, require comprehensive understanding of fluid transport in those systems, such as in the unconventional oil-reservoirs, micro/nano-membrane technologies and lab-on-a-chip applications. The frequently employed transport calculations in literature do not consider any effects related to size or shape of the pore. Instead, dynamically similar flow systems assumed by the porosity of a given medium that an “ability of flow” definition named permeability is employed for a given solid/liquid couple based on the corresponding porosity. However, in such small-scales, liquid flow characteristics diverge from continuum behavior and non-equilibrium effects should be considered to estimate the transport. Furthermore, geometrical parameters of pore structures and networks should be considered, in addition to porosity, for a proper characterization. Hence, pore scale analyses of fluid flow were performed by solving Navier-Stokes equation numerica lly with finite element method in a representative elementary volume. Permeability values were calculated based on the Darcy’s Law, at different pore-to-throat-size ratios, porosities, and velocity slips whose range determined by a literature review. Permeability showed a strong dependence on pore-to-throat-size ratios, and slip conditions. Using the permeability of pores across a wide range of conditions, the Kozeny-Carman (KC) relation was re-considered. An extended phenomenological Kozeny Carman model to predict micro/nanoscale liquid transport as a function of porosity, pore-to-throat size ratio, and slip length was developed. The pore-to-throat-size ratio and slip effects were found substantial on transport, which was successfully predicted by developed model.